A damping valve for shock absorber is applied, for example, to a piston unit or the like of a shock absorber for vehicle and is provided with a piston (valve disk) partitioning one chamber and another chamber for storing working fluid in the shock absorber, a flow passage formed in this piston to allow communication between the one and the other chambers, and a damping force generating element such as a leaf valve for applying resistance to the working fluid passing in this flow passage.
When the piston moves toward the one or the other chamber, the one or the other chamber is pressurized and the working fluid moves between the one and the other chambers through the flow passage. In this way, the shock absorber generates a damping force due to the resistance of the damping force generating element.
Since the damping force generated by the shock absorber for vehicle largely affects the ride quality of a vehicle, it is preferable to provide a damping valve capable of realizing various damping characteristics so that the shock absorber can realize a desired damping characteristic (change in damping force in relation to piston speed).
For example, JP2008-138696A discloses a damping valve for shock absorber in which a retainer is provided to be placed on a piston partitioning one chamber and another chamber.
The above damping valve is provided with an inner peripheral side flow passage configured to include a valve disk through hole formed in an inner peripheral side of the piston and a retainer through hole formed in the retainer and allowing communication between the one and the other chambers, and an outer peripheral side flow passage formed in an outer peripheral side of the piston and allowing communication between the one and the other chambers.
In the above damping valve, even if the flow passages are formed in the inner and outer peripheral sides of the piston, a diameter of a valve seat on which a leaf valve corresponding to the inner peripheral side flow passage is seated can be increased by laminating the leaf valve via the retainer. Thus, it is possible to use the leaf valve having a large diameter and easily deflectable.
Accordingly, a damping coefficient (ratio of the amount of change in damping force to the amount of change in piston speed) of a valve characteristic due to resistance produced when the working fluid passes through a clearance between an outer peripheral part of the leaf valve and the valve seat can be decreased.
Further, a damping force characteristic can be variously changed by replaceably mounting retainers having various dimensions and shapes.